The problems encountered by mechanics when removing large gear boxes, such as third members or differential mechanisms, have caused the loss of a considerable amount of time due to the limited space under a truck in which a mechanic may work for the removal of such large, heavy, unweildy gear boxes or third members. The prior art contains several floor type jacks which are used to support the bottom portion of such mechanisms, particularly third members, such that the third member is resting on an elevating portion of the jack and is therefore frictionally bound thereto. When a large heavy gear box, such as a third member of a truck, is elevated by a jack supporting the third member from the bottom thereof, the weight of the third member and its frictional engagement with the jack prevents it from being easily and readily moved relative to the jack for aligning the mechanism of a third elements, namely spline shafts or the like which are a part of the usual truck differential mechanism. Accordingly, prior art jacks supporting such heavy third members from the bottom thereof are unsatisfactory due to the fact that the frictional engagement of the third members due to the weight bearing on the jack prevents them from being moved easily and readily for alignment of bolt holes on the flanges of the third member relative to flange bolt holes in the banjo housing of the differential and axle structure. Additionally, such frictional movement and engagement of the third member with the jack on which it is carried causes great difficulty in aligning and engaging spline structures which couple the third member mechanisms with the differential mechanisms in the banjo housings of the truck axles. Additionally, prior art jacks have been unweildy due to the fact that there is a very nominal amount of clearance under the truck within which a mechanic may work as compared to the large size and bulk of a differential third member. Therefore, the removal of the third member of overhaul and the replacement thereof has been a time consuming and very difficult problem due to the cramped quarters and also the aforementioned difficulties of supporting the third member or gear box from its bottom portion which is frictionally engaged with the supporting jack in proportion to its weight bearing on the jack.